This is Steven Salzberg's blog on genomics, pseudoscience, medical breakthroughs, higher education, and other topics, including skepticism about unscientific medical practices. Here's where I can say what I really think about abuses and distortions of science, wherever I see them.

Anti-vaxxers are to blame for a new epidemic of measles in the U.S.

Measles is now spreading outward from Disneyland in California, in the worst outbreak in years. The epidemic is fueled by growing enclaves of unvaccinated people.

The CDC reports that in just the past month, 84 people from 14 states contracted measles, a number that is certainly an under-estimate, because the CDC doesn’t record every case. California alone has 59 confirmed cases, most of them linked to an initial exposure in Disneyland. A majority of people who have gotten sick were not vaccinated.

Finally, though, the public seems to be pushing back. Parents are starting to wake up to the danger that the anti-vax movement represents to their children and themselves.

What's sad about this – tragic, really – is that we eliminated measles from the U.S. in the year 2000, thanks to the measles vaccine. As this CDC graph shows, we've had fewer than 100 cases every year since.

But we had 644 cases in 27 states in 2014, the most in 20 years. And 2015 is already on track to be worse. Measles may become endemic in the U.S, circulating continually, thanks to the increasing numbers of unvaccinated people. Until now, each outbreak was caused by someone traveling from abroad and bringing measles to us. The anti-vaccine movement has turned this public health victory into defeat.

Anti-vaxxers have been relentless in the efforts to spread misinformation. Despite overwhelming scientific evidence that vaccines are beneficial, they endlessly repeat a variety false claims, such as

Now, finally, some parents are pushing back. Parents and schools in California, where the epidemic began, are concerned that their children will be exposed to measles from unvaccinated children in schools. And the schools are starting to do something they should have done long ago: send the unvaccinated kids home.

The problem arises from California’s vaccine exemption policy: although public schools require kids to be vaccinated, parents can exempt their kids simply by saying they have a personal objection to vaccination. It’s not just California: only two states, Mississippi and West Virginia, don’t allow parents to claim a philosophical or religious exemption to vaccines And Colorado has the worst rate of vaccination, at just 82%, primarily due to parents claiming a “philosophical” exemption.

These parents are the anti-vaxxers. Thanks to them, we now have large pockets of unvaccinated children through whom epidemics can spread further an faster than we’ve seen in decades. The CDC reports that in 2014, 79% of measles cases in the U.S. involving unvaccinated people were the result of personal belief exemptions.

Anti-vaxxers don't recognize the threat their behavior poses to others, especially to children whose immune systems aren’t functioning properly. CNN reported this week on the case of Rhett Krawitt, a 6-year-old California boy who has gone through 4 years of chemotherapy for childhood leukemia. His leukemia is in remission and he’s back in school, but the treatment wiped out his immunity, and he’s still not ready to get vaccinated. If Rhett gets measles, he might not survive. His father Carl wrote to school district officials to ask them to ban unvaccinated children from school.

Krawitt expects the schools to deny his request.

Meanwhile, the parents who refuse to vaccinate their kids aren’t budging. The New York Times reported on one mother, Crystal McDonald, who refused to vaccinate any of her four children, after “researching the issue” by reading anti-vaccine websites. When their high school sent her daughter home for two weeks, the daughter asked if she could get the measles shot so she could return. As quoted in the Times, McDonald told her daughter “I said ‘No, absolutely not.’ I said I’d rather you miss an entire semester than you get the shot.’”

Where does this breathtaking science denialism come from? It’s been building for years, as I and many others have written. The wave began with a 1998 paper published in The Lancet by Andrew Wakefield, claiming that the MMR vaccine was linked to autism. Wakefield’s work was later shown to be fraudulent, and his claims about the vaccine "dishonest and irresponsible." After lengthy investigations, the paper was retracted and Wakefield lost his medical license. Despite this very public repudiation, Wakefield has stuck to his claims, though, and has spent much of the past 15 years speaking (or perhaps “preaching” would be a better term) to anti-vaccine groups, to whom he is a kind of folk hero.

It’s not just Wakefield, though. Anti-vaccine messages have been broadcast aggressively by the group Generation Rescue, led by former Playboy playmate and MTV host Jenny McCarthy, and by Age of Autism, a group dedicated to the proposition that vaccines cause autism. (Age of Autism is doing it again right now.) And just last summer, Robert F. Kennedy Jr. published a new book further promoting the long-discredited claim that thimerosal causes autism.

Most of the anti-vax crowd have no scientific training or expertise, which might explain (but doesn't excuse) their complete ignorance of the science. Over the past 15 years, dozens of studies involving hundreds of thousands of people have shown convincingly that neither vaccines nor any of the ingredients in them are linked to autism. Vaccines are not only safe, but they are perhaps the greatest public health success in the history of civilization.

“I want to make sure that parents who think that measles is gone and haven't made sure that they or their children are vaccinated are aware that measles is still around and it can be serious. And that MMR vaccine is safe and effective and highly recommended.”

Make no mistake, measles is a very dangerous infection. In the current outbreak, 25% of victims have ended up in the hospital. And it is extremely infectious: the CDC’s Schuchat explained that

“You can catch it [measles] just by being in the same room as a person with measles even if that person left the room because the virus can hang around for a couple of hours.”

Perhaps the Disneyland epidemic, which has now spread to 14 states, will finally convince parents, schools, and state legislatures that they need to insist that children get vaccinated before going to school. Perhaps it will also convince parents to stop listening to nonsense, and choose wisely by getting their children vaccinated against measles. We won this battle before, and we can win it again.